Liz Lange Offers Advice for Jamie Lynn

At 12 weeks pregnant, Jamie Lynn Spears isn't showing – yet. But how should a high-profile 16-year-old dress for the inevitable "bump watch" to come?

"She's a young girl, so I would want to keep [her look] innocent," top maternity designer Liz Lange told PEOPLE at the Great Debaters premiere in New York Wednesday night. "I think little cute dresses and jeans with tight-fitting tee shirts. ... She's 16, and I'd like to see her look her age."

As for how her style should differ from big sis Britney Spears, who frequented Lange's L.A. boutique during her two pregnancies, Lange says, "Britney was into cowboy boots with little dresses. That was her style. I'd like to see Jamie Lynn go a little plainer. [No] belly baring for her!"

Lange continued: "I hope she's ready for this – It's definitely a big step. I know that as a mother myself. But if this is what she wants and what their family wants, then mazel tov."